I'm not even overweight! I have a BMI of about 23, which is within the normal range.
Every time I see my family, they are constantly telling me I am getting fat, and it's driving me nuts because I know I am a healthy weight. I eat pretty healthily, all home cooked food, and monitor what I eat carefully, as I will gain weight if I don't.
I am naturally bigger than my siblings, who have a BMI of about 20-21. My family eat similarly to how I do, its just they happen to be naturally slimmer.
AIBU to tell them to mind their own business as I am a normal healthy weight.